A number of fetal Rhesus monkeys (6 per group) have received intrauterine inoculations with tissues from patients with chronic diseases. Particular emphasis has been placed on Subacute Sclerosing Panencephalitis, Creutzfeldt-Jakob disease, Amyotrophic Lateral Sclerosis, Progressive Multifocal Leukoencephalitis, and Multiple Sclerosis. The animals were inoculated intracerebrally at 100 days gestation. Baby monkeys were delivered by cesarean section and are now in isolation chambers for observation for 3-5 years. The inoculated animals range in age from 38-50 months of age. At this time, no abnormal signs have been observed in any of the monkeys. Surveys of sera and cerebrospinal fluid for elevated antibody titers to a battery of antigens reveal no differences between inoculated animals and controls.